The mobile telephone networks of the prior art have typically had their own independent location management systems, which have not communicated with other radio networks in respect of location management. This has been the case even if several radio systems have been combined to form a single radio network. In GSM systems, location management is standardized so that all GSM systems of different operators can communicate with each other as regards location management. In GSM systems, the location management of a mobile phone is performed by the home network of this mobile phone. The situation is more complicated when several mobile telephone networks of different kinds are combined, e.g. a GSM-type radio network and private radio networks such as PMR-type (Private Mobile Radio) networks. Networks of different types have usually not been able to communicate with each other regarding location management.
A disadvantage of these prior art solutions is that each network requires its own location management system. This is naturally very expensive, as each radio system must have its own location management registers, which are continuously aware of the location of each subscriber.